Editor's note:Julian E. Zelizer is a professor of history and public affairs at Princeton University. He is the author of "Arsenal of Democracy: The Politics of National Security -- From World War II to the War on Terrorism" and of a book on former President Carter, to be published next fall by Times Books.

Princeton, New Jersey (CNN) -- At my local gym Thursday, one of the television sets showed the live CNN broadcast of Rep. Henry Waxman questioning BP CEO Tony Hayward about how so much could have gone wrong.

The problem was, most people at the gym weren't watching. Some of them were tuned in to the other television sets on the wall that broadcast the World Cup. Yet others had their eyes glued to the music video stations that play continuously throughout the day near the Nautilus machines.

The runners on the treadmills had their eyes on the small television monitors on their equipment, each set on the particular show that interested them -- in most cases, not news channels. Near the coffee bar, two men spoke to each other as each stared down at their Blackberries, oblivious to the hearings showing right over their head.

Congressional hearings just aren't what they used to be. We live in a multimedia world that has made it much more difficult for congressional committees to draw attention to their work when they are fulfilling one of the most important roles of the legislative branch: to act as a watchdog by convening hearings.

While, historically, many hearings have fallen flat and have failed to produce any kind of concrete legislative outcome, the added challenge today is that they take place in a media environment where the public has so many choices as to what they should watch that it is almost impossible to gain national attention.

This is a shame, for there have been moments when the nation has been absorbed by congressional hearings that produced extremely important debates over key issues of the day.

In 1966, Sen. William Fulbright of Arkansas, chairman of the Senate Foreign Relations Committee, dragged members of President Lyndon Johnson's administration before his committee to expose some of the weaknesses that were only starting to become apparent in the administration's Vietnam policies.

Although the networks were hesitant to give up lucrative commercial space, the head of CBS News, Fred Friendly, concluded the public should see the debate. On one day when a prominent official testified before the panel, Friendly canceled profitable sitcom reruns of "I Love Lucy," "The McCoys" and "The Dick Van Dyke Show" in the morning anddaytime soap operas and game shows in the afternoon. And if people didn't see the hearings, they certainly saw a clip on the evening newscasts.

The hearings were a turning point in the Vietnam War. Criticism about the war, which had been confined to college campuses, started to spread into middle-class, suburban homes.

Another legendary moment of congressional investigation took place when a special select committee of the U.S. Senate investigated Watergate.

Chaired by the 76-year old Sam Ervin, the venerable conservative Southern Democrat whose background as a constitutional lawyer lent gravity to the proceedings, the committee started its hearings in March in closed session with the former security coordinator of the Committee to Re-Elect the President, James McCord.

During a grueling four-hour meeting, McCord admitted that Attorney General John Mitchell had agreed to the plot to bug Democratic offices at the Watergate complex. Resuming in May, the committee's nationally televised hearings drew huge interest. For six hours a day, tens of millions of Americans tuned in. According to one scholarly study, "57 percent of those questioned believed that the [Ervin] committee was more interested in gaining facts than in discrediting the Nixon Administration, while only 28 percent criticized it."

The shady dealings that Ervin's committee uncovered and the existence of the secret White House tapes ultimately led to the resignation of President Nixon.

The Watergate hearings generated massive concern about the scandal's connection to the White House, helping Americans to connect the dots between the different stories coming out of the Washington press. The hearings fueled structural changes in government, including congressional oversight of federal intelligence agencies, the War Powers resolution, campaign finance reform and independent counsel investigations of executive branch wrongdoing.

When Congress opened its door to television networks in 1977 (the House) and in 1986 (the Senate) and television news started to gain more channels with the creation of CNN in 1980, there were expectations that people would gain a better sense of what the legislative branch actually did.

Congress, through television, would be able to better compete with the presidency and use the power of the televised pulpit to replicate what Fulbright and Ervin accomplished, just on a grander scale. That was the theory.

But history played out differently. Although today the public can watch more congressional hearings than ever, it is difficult to think of any in recent times that match the Fulbright or Ervin committees.

One of the main challenges has been the 24-hour, instantaneous multi-outlet media. With the advent of cable television and then the Internet, Americans have access to many more channels and sites and more types of technology through which to read the news.

Technology has empowered Americans to have more choices about how they want to get their news and whether they want to see something other than the news.

Furthermore, the multiple sources of news produce a steady flow of leaks and information before the hearings even begin. Some of the drama that earlier viewers enjoyed when watching hearings is more difficult to recreate with information already coming out on blogs and other sources. Americans know the story before the hearings begin. While the speed of social media, mobile phones and websites allow for certain statements or gaffes, such as Rep. Joe Barton's apology to BP to spread widely, most of the debate in the hearings, beyond a few soundbites, goes unnoticed.

Whereas viewers saw senators start to put together the truth of the Watergate scandal, this time most citizens will come away with a few controversial statements at best.

Members of Congress have much more trouble shaping national conversations and much more difficulty controlling the flow of information than they did in the period before the 1980s. Legislators such as Waxman, who still believe that the legislative branch has a role to fill in the politics of investigation, might have to start finding new ways to fulfill this historic function.

The opinions expressed in this commentary are solely those of Julian E. Zelizer.